Reports on the number of dead and wounded varied, ranging from seven to 27 dead and 60 to more than 150 wounded.
Police said the first explosion was near the Taqwa Mosque, where Salafist Sheik Salem al-Rafei, a opponent of Syrian President Bashar Assad, was delivering a sermon, The (Beirut) Daily Star reported.
Rafei was not injured.
The second blast occurred minutes later near the Salam Mosque where a sermon was given by Bilal Baroudi, also a Salafist.
Both explosions occurred as hundreds exited the mosques following prayers, The Daily Star said.
"It was as if there was an earthquake; the whole city seemed to be shaking," Nada Fallah, who lives near Salam Mosque, told The Daily Star.
The newspaper said dozens of vehicles near the mosques were ablaze and streets were filled with glass and wreckage, hampering rescue efforts. Residents rushed to help extract the wounded, some of whom were trapped in burning or wrecked vehicles.
Initial damage reports indicated parts of the Taqwa Mosque ceiling collapsed. Reports also indicated several other buildings were damaged.